Window Terminology F.A.Q

Awning Window: A top-hinged window that swings outward for ventilation.

Bay Window: An angled combination of three windows that project out from the wall of the home.

Bow Window: A curved combination of windows that creates a rounded projection.

Casement Window: A side-hinged sash that opens outward.

Double Hung Window: Two operable sashes that move vertically.

Single Hung: Only the bottom sash moves vertically.

Picture Window: A fixed window that does not open.

Geometric: Custom-shaped windows like triangles, circles, and arches.

Oriel: A double-hung style with off-center meeting rails, like a 60/40 split.

Rolling Window: Windows that slide open horizontally.

Hopper: Bottom-hinged window that opens inward.

Patio Door: Sliding door with 2- or 3-lite configurations.

Low-E Glass: Reflects heat while allowing light to pass through.

Tempered Glass: Safety glass that shatters into small, blunt pieces.

Laminated Glass: Two or more panes of glass with a plastic interlayer to prevent shattering.

Obscure Glass: Textured glass for privacy without blocking light.

Argon Gas: Dense inert gas used between glass panes for insulation.

Krypton Gas: Higher-density inert gas used for premium insulation performance.

Double-Strength Glass: Approximately 1/8″ thick, more durable than single-strength.

Single-Strength Glass: Approximately 3/32″ thick, used in smaller window units.

IG Unit (Insulating Glass Unit): Two or more panes sealed together with a spacer between them.

Capillary Tubes: Allow air pressure equalization in IGUs during transit and installation.

Desiccant: Absorbent material in IG spacers that prevents moisture buildup.

Glazing: The process of securing glass inside a window sash.

Dry Glazing: A glazing method using mechanical gaskets or tape, not wet sealant.

Wet Glazing: Uses silicone or sealants to secure the glass.

Visible Light Transmittance: Percentage of visible light that passes through glass.

UV Block: Percentage of ultraviolet radiation blocked by the glass.

Main Frame: The head, sill, and jambs sections of a window.

Head: The top horizontal section of the frame.

Sill: The bottom horizontal section of the frame.

Jamb: The vertical sides of the window frame.

Nailing Fin: A flange used in new construction for attaching the window to the wall opening.

J-Channel: A trim piece used to integrate windows with siding.

Head Expander: A piece used to fill gaps between the window head and rough opening.

Sill Extender: Covers the space between the window sill and the rough opening.

Stucco Fin: A trim piece used for stucco installations.

Beveled/Coved/Raised Exterior: Decorative trim profiles to enhance appearance.

Cam Lock & Keeper: Locking mechanism that secures the window sash.

Lift Handle / Rail: Used to raise or lower window sashes.

Pull Handle / Rail / Stile: Used for opening and closing sliding windows.

Vent-lok: Allows sash to remain partially open for ventilation.

Tilt Latch: Releases sash for inward tilting and cleaning.

Sash: The moveable or fixed frame that holds the glass.

Sash Alignment / Pivot System: Ensures smooth tilting and operation of sashes.

U-Value: Rate of heat transfer; lower is better.

R-Value: Resistance to heat flow; higher is better.

Solar Heat Gain Coefficient: Measures how much solar radiation passes through.

Shading Coefficient: Compares solar heat gain to that of 1/8” clear glass.

Condensation Resistance: Measures window’s ability to resist moisture build-up.

Total Unit U-/R-Values: Reflects performance across full unit, not just glass center.

Weep Holes / Slots / Flaps: Allow water to escape while keeping insects out.

Spacer: Maintains distance between panes in insulating glass.

Mesh: Screen fabric, typically fiberglass or aluminum.

Extruded / Roll-formed Screen Frame: Fabrication types for screen frame durability.

Hook Accessory: Snap-in components that simplify window installation.

Wood Blocks: Plywood spacers used for shimming and joining multiple units.